The present invention relates to a 17.alpha.-dihydroequilin hapten, to an immunogen for preparing an antiserum especially suited for use in the radioimmunoassay of 17.alpha.-dihydroequilin and to the antiserum. The invention also relates to a method of radioimmunoassay using the antiserum.
17.alpha.-Dihydroequilin, in the form of its 3-sulfate salt, is a major component of conjugated (equine) estrogens which are used for the treatment of menopausal disorders. The three major components of conjugated (equine) estrogens by weight are estrone sulfate (about 50%), equilin sulfate (about 25%) and 17.alpha.-dihydroequilin 3-sulfate (about 15%). Although 17.alpha.-dihydroequilin is known to be a potent estrogen, little is known about its pharmacologic action and metabolism. A tool, which would be extremely useful to acquire knowledge about these parameters, would be a specific antiserum for 17.alpha.-dihydroequilin.
Specific antisera have been developed for such estrogens as estrone, 17.beta.-estradiol and estriol, for example, see P. N. Rao and P. H. Moore, Jr., Steroids, 29, 461 (1977). An antiserum also has been reported for equilin, see P. G. Whittaker et al., The Lancet, 1, 14 (1980) and M. R. A. Morgan et al., J. Steroid Biochem., 13, 551 (1980). This latter antiserum is derived from an immunogen obtained by attaching a steroid to an immunological carrier by means of an ester linkage, a form of attachment different from that of the present immunogen. Notwithstanding these developments, a specific antiserum for 17.alpha.-dihydroequilin had yet to be developed prior to the development of the antiserum of this invention.
Accordingly, the present invention fulfills the above-noted need by providing a specific antiserum for the radioimmunoassay of 17.alpha.-dihydroequilin. The antiserum has a minimum of cross reaction with other steroids found in serum and/or steroids which form the conjugates present in conjugated estrogens.